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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Osmium Isotope and Highly Siderophile Element Compositions of Lunar Orange and Green Glasses

The absolute and relative abundances of the highly siderophile elements (HSE) present in planetary mantles are primarily controlled by: 1) silicate-metal partitioning during core-mantle differentiation, 2) the subsequent addition of HSE to mantles via continued planetary accretion. Consequently, constraints on the absolute and relative abundances of the HSE in the lunar mantle will provide unique insights to the formation and late accretionary history of not only the Moon, but also Earth. Determining the HSE content of the lunar mantle, however, has proven difficult, because no bona fide mantle rocks have been collected from the moon. The only materials presently available for constraining mantle abundances are lunar volcanic rocks. Lunar basalts typically have very low concentrations of HSE and highly fractionated HSE patterns. Because of our extremely limited understanding of mantle melt partitioning of the HSE, even for terrestrial systems, extrapolations to mantle compositions from basaltic compositions are difficult, except possibly for the less compatible HSE Pt and Pd. Primitive, presumably less fractionated materials, such as picritic glasses are potentially more diagnostic of the lunar interior. Here we report Os isotopic composition data and Re, Os, Ir, Ru, Pt and Pd concentration data for green glass (15426,164) and orange glass (74001,1217). As with previous studies utilizing neutron activation analysis, we are examining different size fractions of the spherules to assess the role of surface condensation in the generation of the HSE abundances.

Walker, R. J.↗
NASA NTRS2004

Flexible Microsensor Array for the Root Zone Monitoring of Porous Tube Plant Growth System

Control of oxygen and water in the root zone is vital to support plant growth in the microgravity environment. The ability to control these sometimes opposing parameters in the root zone is dependent upon the availability of sensors to detect these elements and provide feedback for control systems. In the present study we demonstrate the feasibility of using microsensor arrays on a flexible substrate for dissolved oxygen detection, and a 4-point impedance microprobe for surface wetness detection on the surface of a porous tube (PT) nutrient delivery system. The oxygen microsensor reported surface oxygen concentrations that correlated with the oxygen concentrations of the solution inside the PT when operated at positive pressures. At negative pressures the microsensor shows convergence to zero saturation (2.2 micro mol/L) values due to inadequate water film formation on porous tube surface. The 4-point microprobe is useful as a wetness detector as it provides a clear differentiation between dry and wet surfaces. The unique features of the dissolved oxygen microsensor array and 4-point microprobe include small and simple design, flexibility and multipoint sensing. The demonstrated technology is anticipated to provide low cost, and highly reliable sensor feedback monitoring plant growth nutrient delivery system in both terrestrial and microgravity environments.

Sathyan, Sandeep↗
NASA NTRS2002

Growth and maturational changes in dense fibrous connective tissue following 14 days of rhGH supplementation in the dwarf rat

The purpose of this study was to investigate the impact of recombinant human growth hormone (rhGH) on patella tendon (PT), medial collateral ligament (MCL), and lateral collateral ligament (LCL) on collagen growth and maturational changes in dwarf GH-deficient rats. Twenty male Lewis mutant dwarf rats, 37 days of age, were randomly assigned to Dwarf + rhGH (n = 10) and Dwarf + vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt twice daily for 14 days. rhGH administration stimulated dense fibrous connective tissue growth, as demonstrated by significant increases in hydroxyproline specific activity and significant decreases in the non-reducible hydroxylysylpyridinoline (HP) collagen cross-link contents. The increase in the accumulation of newly accreted collagen was 114, 67, and 117% for PT, MCL, and LCL, respectively, in 72 h. These findings suggest that a short course rhGH treatment can affect the rate of new collagen production. However, the maturation of the tendon and ligament tissues decreased 18-25% during the rapid accumulation of de novo collagen. We conclude that acute rhGH administration in a dwarf rat can up-regulate new collagen accretion in dense fibrous connective tissues, while causing a reduction in collagen maturation. Copyright 2002 Elsevier Science Ltd.

NASA Discipline Musculoskeletal↗
NASA NTRS2005

Isotopic And Geochemical Investigations Of Meteorites

The primary goals of our research over the past four years are to constrain the timing of certain early planetary accretion/differentiation events, and to constrain the proportions and provenance of materials involved in these processes. This work was achieved via the analysis and interpretation of long- and short-lived isotope systems, and the study of certain trace elements. Our research targeted these goals primarily via the application of the Re-187, Os-187, Pt-190 Os-186 Tc-98 Ru-99 and Tc-99 Ru-99 isotopic systems, and the determination/modeling of abundances of the highly siderophile elements (HSE; including Re, Os, Ir, Ru, Pd, Pt, and maybe Tc). The specific events we examined include the segregation and crystallization histories of asteroidal cores, the accretion and metamorphic histories of chondrites and chondrite components, and the accretionary and differentiation histories of Mars and the Moon.

Walker, Richard J.↗
NASA NTRS1995

Hydrogen Effects on GaAs, Status and Progress

It has been observed that GaAs devices in hermetically sealed packages when exposed to temperatures as low as 125oC can exhibit unacceptable degradation in both RF and DC characteristics. The source of the problem was found to be hydrogen that has been absorbed in the package's metals (Kovar, plating, etc.) and converted into atomic hydrogen within the Pt metallization of the gate structure. Subsequently, atomic hydrogen diffuses into the channel region of the FET structure and neutralizes the Si donors, resulting in a degradation of the device characteristics. Most of the data indicates the onslaught of the problem to occur after 500 hours at 125oC. This onslaught has been observed to be dependent on the thickness and processing conditions of the passivation layer, the sealing environment, and the amount of Pt or Pd in the gate structure of the device.

Hydrogen GaAs↗
NASA NTRS1995

Performance of PEM Liquid-Feed Direct Methanol-Air Fuel Cells

A direct methanol-air fuel cell operating at near atmospheric pressure, low-flow rate air, and at temperatures close to 60oC would tremendously enlarge the scope of potential applications. While earlier studies have reported performance with oxygen, the present study focuses on characterizing the performance of a PEM liquid feed direct methanol-air cell consisting of components developed in house. These cells employ Pt-Ru catalyst in the anode, Pt at the cathode and Nafion 117 as the PEM. The effect of pressure, flow rate of air and temperature on cell performance has been studied. With air, the performance level is as high as 0.437 V at 300 mA/cm2 (90oC, 20 psig, and excess air flow) has been attained. Even more significant is the performance level at 60oC, 1 atm and low flow rates of air (3-5 times stoichiometric), which is 0.4 V at 150 mA/cm2. Individual electrode potentials for the methanol and air electrode have been separated and analyzed. Fuel crossover rates and the impact of fuel crossover on the performance of the air electrode have also been measured. The study identifies issues specific to the methanol-air fuel cell and provides a basis for improvement strategies.

Methanol-Air Fuel↗
NASA NTRS2007

Highly Sideophile Element Abundance Constraints on the Nature of the Late Accretionary Histories of Earth, Moon and Mars

The highly siderophile elements (HSE) include Re, Os, Ir, Ru, Pt and Pd. These elements are initially nearly-quantitatively stripped from planetary silicate mantles during core segregation. They then may be re-enriched in mantles via continued accretion sans continued core segregation. This suite of elements and its included long-lived radiogenic isotopes systems (Re-187 (right arrow) Os-187; Pt-190 (right arrow) Os-186) can potentially be used to fingerprint the characteristics of late accreted materials. The fingerprints may ultimately be useful to constrain the prior nebular history of the dominant late accreted materials, and to compare the proportion and genesis of late accretionary materials added to the inner planets. The past ten years have seen considerable accumulation of isotopic and compositional data for HSE present in the Earth's mantle, lunar mantle and impact melt breccias, and Martian meteorites. Here we review some of these data and consider the broader implications of the compiled data.

Walker, R. J.↗
NASA NTRS2007

Sulfur and Moisture Effects on Alumina Scale and TBC Spallation

It has been well established that a few ppmw sulfur impurity may segregate to the interface of thermally grown alumina scales and the underlying substrate, resulting in bond degradation and premature spallation. This has been shown for NiAl and NiCrAl-based alloys, bare single crystal superalloys, or coated superalloys. The role of reactive elements (especially Y) has been to getter the sulfur in the bulk and preclude interfacial segregation. Pt additions are also very beneficial, however a similar thermodynamic explanation does not apply. The purpose of the present discussion is to highlight some observations of these effects on Rene'142, Rene'N5, PWA1480, and PWA1484. For PWA1480, we have mapped cyclic oxidation and spallation in terms of potential sulfur interfacial layers and found that a cumulative amount of about one monolayer is sufficient to degrade long term adhesion. Depending on substrate thickness, optimum performance occurs if sulfur is reduced below about 0.2-0.5 ppmw. This is accomplished in the laboratory by hydrogen annealing or commercially by melt-fluxing. Excellent 1150 C cyclic oxidation is thus demonstrated for desulfurized Rene'142, Rene'N5, and PWA1484. Alternatively, a series of N5 alloys provided by GE-AE have shown that as little as 15 ppmw of Y dopant was effective in providing remarkable scale adhesion. In support of a Y-S gettering mechanism, hydrogen annealing was unable to desulfurize these alloys from their initial level of 5 ppmw S. This impurity and critical doping level corresponds closely to YS or Y2S3 stoichiometry. In many cases, Y-doped alloys or alloys with marginal sulfur levels exhibit an oxidative sensitivity to the ambient humidity called Moisture-Induced Delayed Spallation (MIDS). After substantial scale growth, coupled with damage from repeated cycling, cold samples may spall after a period of time, breathing on them, or immersing them in water. While stress corrosion arguments may apply, we propose that the underlying cause is related to a hydrogen embrittlement reaction: Al alloy + 3 H2O = Al(OH)3 + 3H(+) + 3e(-). This mechanism is derived from an analogous moisture-induced hydrogen embrittlement mechanism originally shown for Ni3Al and FeAl intermetallics. Consequently, a cathodic hydrogen charging technique was used to demonstrate that electrolytic de-scaling occurs for these otherwise adherent alumina scales formed on Y-doped Rene'N5, in support of hydrogen effects. Finally, some TBC observations are discussed in light of all of the above. Plasma sprayed 8YSZ coatings, produced on PWA1484 without a bond coat, were found to survive more than 1000 1-hr cycles at 1100 C when desulfurized to below 0.1 ppmw. At higher sulfur (1.2 ppmw) levels, moisture sensitivity and delayed TBC failure, referred to as Desk Top Spallation, occurred at just 200 hr. Despite a large degree of scatter, a factor of 5 in life improvement is indicated for desulfurized samples in cyclic furnace tests, confirming the beneficial effect of low sulfur alloys on model TBC systems. (DTS and moisture effects are also observed on commercially applied PVD 7YSZ coatings on Rene'N5+Y with Pt-aluminide bond coats). These types of catastrophic failure were subverted on the model system by segmenting the substrate into a network of 0.010 high ribs, spaced in. apart, prior to plasma spraying. No failures occurred after 1000 cycles at 1150 C or after 2000 cycles at 1100 C, even after water immersion. The benefit is described in terms of elasticity models and a critical buckling stress.

Smialek, James L.↗
NASA NTRS2007

Marine Boundary Layer Cloud Properties From AMF Point Reyes Satellite Observations

Cloud Diameter, C(sub D), offers a simple measure of Marine Boundary Layer (MBL) cloud organization. The diurnal cycle of cloud-physical properties and C(sub D) at Pt Reyes are consistent with previous work. The time series of C(sub D) can be used to identify distinct mesoscale organization regimes within the Pt. Reyes observation period.

Jensen, Michael↗
NASA NTRS2007

Transient Numerical Modeling of Catalytic Channels

This paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a lumped two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the first case. Finally, the results show that different initial surface-species distribution leads to different steady-states under certain conditions. These results demonstrate the utility of a lumped two-phase model of a transient catalytic combustor with detailed chemistry.

Struk, Peter M.↗
NASA NTRS2007

Effects of Stoichiometry on Transformation Temperatures and Actuator-Type Performance of NiTiPd and NiTiPdX High-Temperature Shape Memory Alloys

High-temperature shape memory NiTiPd and NiTiPdX (X=Au, Pt, Hf) alloys were produced with titanium equivalent (Ti+Hf) compositions of 50.5, 50.0, 49.5, and 49.0 at.%. Thermo-mechanical testing in compression was used to evaluate the transformation temperatures, transformation strain, work output, and permanent deformation behavior of each alloy to study the effects of quaternary alloying and stoichiometry on high-temperature shape memory alloy behavior. Microstructural evaluation showed the presence of second phases for all alloy compositions. No load transformation temperatures in the stoichiometric alloys were relatively unchanged by Au and Pt substitutions, while the substitution of Hf for Ti causes a drop in transformation temperatures. The NiTiPd, NiTiPdAu and NiTiPdHf alloys exhibited transformation temperatures that were highest in the Ti-rich compositions, slightly lower at stoichiometry, and significantly reduced when the Ti equivalent composition was less than 50 at.%. For the NiTiPdPt alloy, transformation temperatures were highest for the Ti-rich compositions, lowest at stoichiometry, and slightly higher in the Ni-rich composition. When thermally cycled under constant stresses of up to 300 MPa, all of the alloys had transformation strains, and therefore work outputs, which increased with increasing stress. In each series of alloys, the transformation strain and thus work output was highest for stoichiometric or Ti-rich compositions while permanent strain associated with the constant-load thermal cycling was lowest for alloys with Ni-equivalent-rich compositions. Based on these results, basic rules for optimizing the composition of NiTiPd alloys for actuator performance will be discussed.

Bigelow, Glen S.↗
NASA NTRS2009

Cryogenic Piezoelectric Actuator

In this paper, PMN-PT single crystal piezoelectric stack actuators and flextensional actuators were designed, prototyped and characterized for space optics applications. Single crystal stack actuators with footprint of 10 mm x10 mm and the height of 50 mm were assembled using 10 mm x10mm x0.15mm PMN-PT plates. These actuators showed stroke > 65 - 85 microns at 150 V at room temperature, and > 30 microns stroke at 77 K. Flextensional actuators with dimension of 10mm x 5 mm x 7.6 mm showed stroke of >50 microns at room temperature at driving voltage of 150 V. A flextensional stack actuator with dimension of 10 mm x 5 mm x 47 mm showed stroke of approx. 285 microns at 150 V at room temperature and > 100 microns at 77K under driving of 150 V should be expected. The large cryogenic stroke and high precision of these actuators are promising for cryogenic optics applications.

Jiang, Xiaoning↗
NASA NTRS2010

Catalyst for Carbon Monoxide Oxidation

In many applications, it is highly desirable to operate a CO2 laser in a sealed condition, for in an open system the laser requires a continuous flow of laser gas to remove the dissociation products that occur in the discharge zone of the laser, in order to maintain a stable power output. This adds to the operating cost of the laser, and in airborne or space applications, it also adds to the weight penalty of the laser. In a sealed CO2 laser, a small amount of CO2 gas is decomposed in the electrical discharge zone into corresponding quantities of CO and O2. As the laser continues to operate, the concentration of CO2 decreases, while the concentrations of CO and O2 correspondingly increase. The increasing concentration of O2 reduces laser power, because O2 scavenges electrons in the electrical discharge, thereby causing arcing in the electric discharge and a loss of the energetic electrons required to boost CO2 molecules to lasing energy levels. As a result, laser power decreases rapidly. The primary object of this invention is to provide a catalyst that, by composition of matter alone, contains chemisorbed water within and upon its structure. Such bound moisture renders the catalyst highly active and very long-lived, such that only a small quantity of it needs to be used with a CO2 laser under ambient operating conditions. This object is achieved by a catalyst that consists essentially of about 1 to 40 percent by weight of one or more platinum group metals (Pt, Pd, Rh, Ir, Ru, Os, Pt being preferred); about 1 to 90 percent by weight of one or more oxides of reducible metals having multiple valence states (such as Sn, Ti, Mn, Cu, and Ce, with SnO2 being preferred); and about 1 to 90 percent by weight of a compound that can bind water to its structure (such as silica gel, calcium chloride, magnesium sulfate, hydrated alumina, and magnesium perchlorate, with silica gel being preferred). Especially beneficial results are obtained when platinum is present in the catalyst composition in an amount of about 5 to 25 (especially 7) percent by weight, SnO2 is present in an amount of about 30 to 40 (especially 40) percent by weight, and silica gel is present in an amount of 45 to 55 (especially 50) percent by weight. The composition of this catalyst was suggested by preliminary experiments in which a Pt/SnO2 catalyst was needed for bound water to enhance its activity. These experimental results suggested that if the water were bound to the surface, this water would enhance and prolong catalyst activity for long time periods. Because the catalyst is to be exposed to a laser gas mixture, and because a CO2 laser can tolerate only a very small amount of moisture, a hygroscopic support for the catalyst would provide the needed H2O into the gas. Silica gel is considered to be superior because of its property to chemisorb water on its surface over a wide range of moisture content.

Davis, Patricia↗
NASA NTRS2011

High Pressure and Temperature Core Formation as an Alternative to the "Late Veneer" Hypothesis

The highly siderophile elements (HSE; Re, Au and the Platinum Group Elements - Pd Pt, Rh, Ru, Ir, Os) are commonly utilized to constrain accretion processes in terrestrial differentiated bodies due to their affinity for FeNi metal [1]. These eight elements exhibit highly siderophile behavior, but nonetheless have highly diverse metal-silicate partition coefficients [2]. Therefore the near chondritic relative concentrations of HSEs in the terrestrial and lunar mantles, as well as some other bodies, are attributed to late accretion rather than core formation [1]. Evaluation of competing theories, such as high pressure metal-silicate partitioning or magma ocean hypotheses has been hindered by a lack of relevant partitioning data for this group of eight elements. In particular, systematic studies isolating the effect of one variable (e.g. temperature or melt compositions) are lacking. Here we undertake new experiments on all eight elements, using Fe metal and FeO-bearing silicate melts at fixed pressure, but variable temperatures. These experiments, as well as some additional planned experiments should allow partition coefficients to be more accurately calculated or estimated at the PT conditions and compositions at which core formation is thought to have occurred.

Righter, Kevin↗
NASA NTRS2011

Parametric Testing of Launch Vehicle FDDR Models

For the safe operation of a complex system like a (manned) launch vehicle, real-time information about the state of the system and potential faults is extremely important. The on-board FDDR (Failure Detection, Diagnostics, and Response) system is a software system to detect and identify failures, provide real-time diagnostics, and to initiate fault recovery and mitigation. The ERIS (Evaluation of Rocket Integrated Subsystems) failure simulation is a unified Matlab/Simulink model of the Ares I Launch Vehicle with modular, hierarchical subsystems and components. With this model, the nominal flight performance characteristics can be studied. Additionally, failures can be injected to see their effects on vehicle state and on vehicle behavior. A comprehensive test and analysis of such a complicated model is virtually impossible. In this paper, we will describe, how parametric testing (PT) can be used to support testing and analysis of the ERIS failure simulation. PT uses a combination of Monte Carlo techniques with n-factor combinatorial exploration to generate a small, yet comprehensive set of parameters for the test runs. For the analysis of the high-dimensional simulation data, we are using multivariate clustering to automatically find structure in this high-dimensional data space. Our tools can generate detailed HTML reports that facilitate the analysis.

Schumann, Johann↗
NASA NTRS2011

Preflight and In-Flight Exercise Conditions for Astronauts on the International Space Station

The physiological demands of spaceflight require astronauts to have certain physical abilities. They must be able to perform routine and off-nominal physical work during flight and upon re-entry into a gravity environment to ensure mission success, such as an Extra Vehicular Activity (EVA) or emergency egress. To prepare the astronauts for their mission, a Wyle Astronaut Strength Conditioning and Rehabilitation specialist (ASCR) works individually with the astronauts to prescribe preflight strength and conditioning programs and in-flight exercise, utilizing Countermeasure Systems (CMS) exercise hardware. PURPOSE: To describe the preflight and in-flight exercise programs for ISS crewmembers. METHODS: Approximately 2 years before a scheduled launch, an ASCR is assigned to each astronaut and physical training (PT) is routinely scheduled. Preflight PT of astronauts consists of carrying out strength, aerobic and general conditioning, employing the principles of periodization. Exercise programs are prescribed to the astronauts to account for their individual fitness levels, planned mission-specific tasks, areas of concern, and travel schedules. Additionally, astronauts receive instruction on how to operate CMS exercise hardware and receive training for microgravity-specific conditions. For example, astronauts are scheduled training sessions for the International Space Station (ISS) treadmill (TVIS) and cycle ergometer (CEVIS), as well as the Advanced Resistive Exercise Device (ARED). In-flight programs are designed to maintain or even improve the astronauts pre-flight levels of fitness, bone health, muscle strength, power and aerobic capacity. In-flight countermeasure sessions are scheduled in 2.5 h blocks, six days a week, which includes 1.5 h for resistive training and 1 h for aerobic exercise. CONCLUSIONS: Crewmembers reported the need for more scheduled time for preflight training. During flight, crewmembers have indicated that the in-flight exercise is sufficient, but would like more reliable and capable hardware.

Guilliams, Mark E.↗
NASA NTRS2012

Experimental Study of the Partitioning of Siderophile Elements in a Crystallizing Lunar Magma Ocean

The distributions of trace elements between the lunar interior and pristine crustal rocks were controlled by the composition of starting materials, lunar core formation, and crystallization of the lunar magma ocean (LMO) [1]. This study focuses on the partitioning of highly siderophile elements (HSE) including Re, Os, Ir, Ru, Pt, Rh, Pd and Au as well as the moderately siderophile elements Mo and W, and the lithophile elements of Hf and Sr. Our experiments also include Ga, which can be slightly siderophile, but is mostly considered to be chalcophile. Partitioning of these elements is not well known at the conditions of a crystallizing LMO. Previous studies of HSE partitioning in silicate systems have yielded highly variable results for differing oxygen fugacity (fO2) and pressure [2-4]. For example, under certain conditions Pt is compatible in clinopy-roxene [2] and Rh and Ru are compatible in olivine [3]. The silicate compositions used for these experiments were nominally basaltic. Ruthenium, Rh, and Pd are incompatible in plagioclase under these conditions[4]. However, this latter study was done at extremely oxidizing conditions and at atmospheric pressure, possibly limiting the applicability for consideration of conditions of a crystallizing LMO. In this study we address the effects of pressure and oxygen fugacity on the crystal/liquid partition coefficients of these trace elements. We are especially interested in the plagioclase/melt partition coefficients so that it may be possible to use reverse modeling to constrain the concentrations of these elements in the lunar mantle through their abundances in pristine crustal rocks.

Galenas, M.↗
NASA NTRS2012

Coordinated STEM/FIB/NanoSIMS Analyses of Presolar Silicates in Comet Dust and Primitive Meteorites

Silicate grains were among the most abundant mineralogical building blocks of our Solar System. These grains were the detritus from earlier generations of stars that have been recycled in the early solar nebula. Rare sub-micrometer survivors of this processing have been identified in meteorites, micrometeorites and interplanetary dust particles (IDPs). These silicate grains are recognized as presolar in origin because of their extremely anomalous isotopic compositions that reflect nucleosynthetic processes in their stellar sources (evolved stars, novae and supernovae). We perform coordinated chemical, mineralogical and isotopic studies of these grains to determine their origins and histories. We examine the complex mineralogy and petrography of presolar silicates using imaging, diffraction and chemical data obtained from thin sections with the JSC JEOL 2500 field-emission STEM equipped with a Noran thin window energy dispersive x-ray (EDX) spectrometer and a Gatan Tridiem GIF. Quantitative element x-ray maps (spectrum images) are acquired by rastering a 4 nm incident probe whose dwell time is minimized to avoid beam damage and element diffusion during mapping. Successive image layers are acquired and combined in order to achieve approx 1% counting statistics for major elements. The IDP samples are prepared by ultramicrotomy of particles embedded in epoxy or elemental sulfur. After EDX mapping, the sections are subjected to C, N, and O isotopic imaging with the JSC NanoSIMS 50L ion microprobe. We prepare sections of some meteorite grains using the JSC FEI Quanta 3D focused ion beam (FIB) instrument. The specimen surface is protected from the FIB milling process by layers of electron beam-deposited C and Pt followed by an ion-deposited Pt layer. We also use the FIB to preferentially remove surrounding grains to reduce the background in subsequent NanoSIMS measurements. For mineralogical studies, we again employ the FIB instrument to deposit a protective cap over the grain of interest and then extract the grain and thin it to electron transparency for TEM analysis.

Keller, Lindsay↗